In a civil engineering work site or a quarry site of a mine, various working vehicles such as a dump truck and an excavator are operated. Particularly, a superjumbo working vehicle is used in a mine. Since such a working vehicle has a vehicle width, a vehicle height, and a longitudinal length noticeably larger than those of a general vehicle, it is difficult for an operator to check and recognize a peripheral circumstance by a side mirror and the like.
There is known a collision preventing system which shows a peripheral circumstance of a machine to an operator and prevents a collision between the machine and an obstacle. As the collision preventing system, the machine includes radar devices as a plurality of obstacle sensors (for example, Patent Literature 1).